Just added fuel for first time to 02 xstar (obviously just got the boat..). Gas cap was REALLY hard to remove, and as I was unscrewing it, when the seal finally started to break I could hear a LOT of air rushing by the seal. I don't mean a small psst like popping a soda can. Like 5 full seconds of whooosh. I assume it was air rushing into the tank, and I also assume it was suction created by gallons of fuel being pumped out of the tank and no air being allowed to come into the tank to take that space that the fuel used to occupy.. Is this normal? Should a check-valve allow air into the tank to prevent this? Or is the system designed to run with negative pressure in the tank and a sensor monitors the negative pressure and triggers a check engine light if the negative pressure is lost, indicating a compromise in the system allowing air in, or possibly fuel out???